Production of thin film photovoltaic (PV) modules (also referred to as “solar panels”) typically involves conveyance of a substrate, such as a glass panel, into and out of a vapor deposition chamber wherein a thin film layer (generally recognized in the industry as less than 10 um) of a semiconductor material, such as cadmium telluride (CdTe), is deposited onto the surface of the substrate. The deposition process may be any known process, for example a close space sublimation (CSS) system or chemical vapor deposition (CVD) system.
Viewports or “windows” are typically provided in the walls of the deposition chambers or conveying structures of the deposition system for any number of reasons. For example, the viewports may provide a means for visual inspection of the process, or may be configured to provide an input to control equipment that controls various process parameters, such as conveyor speed, and the like. These conventional viewports are, however, typically formed from glass or a glass composition and are prone to condensation or build-up of the sublimated material from the deposition or conveyor chambers. This situation requires frequent shutdown of the system for removal and cleaning or replacement of the viewports.
Shuttered viewports are known in the industry to protect the viewports from exposure to the sublimated material. However, these devices are of limited use because the shutters must be closed to function, which renders the optical viewport inoperable.
Roll-film viewports are also known. These devices operate by providing a layer of transparent protective film over the viewport optics. The film material is provided in roll form and, as the film becomes obscured by condensate, the film is advance from the roll so that a “clean” section of film is positioned in front of the viewport optics. These devices, however, require periodic maintenance and shutdown of the deposition system to replace the film material.
It is also known to heat the viewports to reduce the condensate levels and extend the time between cleaning maintenance procedures. In this regard, various references describe heated viewports for deposition chambers or equipment. Reference is made, for example to U.S. Pat. Nos. 5,129,994; 5,977,526 and 6,367,415. The heated viewports described in these references, however, are not particularly well suited for active sensing systems and have limited functionality.
Accordingly, there exists a need for an improved viewport detection assembly that is particularly suited for active detection of substrates conveyed through a vapor deposition system. The present invention relates to a heated viewport assembly that serves this purpose.